In recent years, in the mechanical field, so-called fiber-reinforced resin materials containing a matrix resin and reinforcing fibers such as carbon fibers have attracted attention. Due to the fact that the fibers are dispersed in the matrix resin, these fiber-reinforced resin materials are excellent in tensile modulus, tensile strength, impact resistance, and the like, and thus have been studied for structural members of automobiles and the like. Among these, fiber-reinforced resin materials in which the matrix resin is a thermoplastic resin, that is, fiber-reinforced thermoplastic resin materials are excellent in mass productivity such as in molding as compared with fiber-reinforced resin materials with a thermosetting resin, and therefore, have been studied in many fields. In addition, the fiber-reinforced thermoplastic resin materials are molded into a desired shape with high productivity by various molding methods such as injection molding and compression molding, and therefore, are suitable for a wide range of applications from large parts to small parts. In particular, a fiber-reinforced resin shaped product containing reinforcing fibers and a thermoplastic resin as a matrix and having grains on at least a part of a surface thereof (hereinafter abbreviated as a shaped product with grains in some cases) has an excellent surface appearance which gives a high-class feeling, and is suitable for use on an exterior part of a product.
For example, PTL 1 discloses a fiber-reinforced resin shaped product having grains on a surface thereof, having a high surface appearance, and having an excellent strength caused by containing reinforcing fibers having a relatively long fiber length, and a method for producing the shaped product with high productivity by compression-molding a fiber-reinforced thermoplastic resin material.
Among the fiber-reinforced thermoplastic resin materials, crystalline resins exhibit high heat resistance, good chemical resistance, and high fluidity due to crystallinity as compared with amorphous resins. Thus, the crystalline resins have been widely adopted for large parts or thin parts which require these properties. In particular, in a case of compression-molding a fiber-reinforced crystalline resin material whose matrix is a crystalline thermoplastic resin, a processing temperature may be set near a crystallization temperature to maximize crystallinity of the resin. The crystallization temperature is a temperature equal to or higher than a glass transition temperature. In a case of compression-molding the fiber-reinforced crystalline resin material at such a temperature, although also affected by fluidity or molding shrinkage rate thereof, since a transfer property of a grained shape from a mold having the grained shape (hereinafter, in a case of a grained shape part, strictly, may be also abbreviated as a grained shape) is significantly improved, a surface of the fiber-reinforced crystalline resin shaped product having grains on at least a part of a surface thereof sticks to a surface of the mold, and there are some cases where a shaped product with grains and having an optically uniform and good appearance, is not obtained.
Further, recently, a production method which includes compression-molding a fiber-reinforced amorphous resin material, in which an amorphous thermoplastic resin is used as a matrix, using a mold having a grained shape and temperature-controlled to a processing temperature equal to or higher than a glass transition temperature of the amorphous thermoplastic resin, cooling the mold to a temperature equal to or lower than the glass transition temperature with the mold closed, and then releasing a shaped product with grains from the mold, namely, a so-called heat-and-cool compression molding has been used. In that case, since a transfer property of a grained shape from the mold having the grained shape is significantly improved, for the reason as described above, there are some cases where a shaped product with grains and having an optically uniform and good appearance, is not obtained.
As described above, there remains a problem in obtaining a fiber-reinforced thermoplastic resin shaped product having an optically uniform and good appearance and having grains on at least a part of a surface thereof.
As a measure for obtaining a uniform and good appearance with grains, a method of using an inorganic reinforced polyamide resin composition formed of, for example, a polycapramide resin, a polyamide resin other than the polycapramide resin, and an inorganic reinforcing material has been proposed (see PTL 2). However, this technique is a technology of blending a different type of polyamide resin into the polycapramide resin so that transfer property of grains from a mold to a shaped product during molding becomes uniform, and it is hard to say that a case where a transfer property of the entire composition is increased is considered. In addition, a method of obtaining a thermosetting resin shaped product that can be compression-molded with good releasability and has a glossy surface according to specifications has been proposed, in which, after engraving a cavity with a desired product shape on a mold base material, spherical particles are sprayed onto a surface of the cavity and angular apex portions of unevenness on the surface of the cavity generated by the engraving are ground to form a satin-finished face, and a thermosetting resin is molded using the mold with a plating layer (plating film) applied to a surface of the satin-finished surface (see PTL 3). However, this technique is directed to compression-molding of a thermosetting resin. Thus, it is not considered to be applied to compression-molding of a fiber-reinforced thermoplastic resin body having a high molding pressure, and also a grinding surface thereof, on which large unevenness remain after the engraving of cavity, is satin-finished. From these facts, it is far from an optically uniform and good appearance with grains of the present invention. In addition, a method for producing a shaped product has been proposed, in which an alicyclic structure-containing polymer resin is molded using a mold that is formed of a mold A having a concave portion and a mold B having a convex portion, in which a cylindrical cavity can be formed by the convex portion and the concave portion, and a surface of the convex portion has a Rockwell hardness C of 40 or more, a ten-point average roughness of greater than 0.5 μm and 2.5 μm or less, and a draft angle of 0° to 5° (see PTL 4). However, this technique is intended to avoid scratches generated due to damages of a surface of a cylindrical shaped product having a small draft angle caused by the mold in a case where the shaped product is released from the mold, and an object thereof is greatly deviated from that of the present invention which is to obtain an optically uniform and good appearance with grains. From the above, the technologies which have been proposed so far are not necessarily technologies specialized for improving an appearance of a shaped product with grains, and there is room for improvement.